What is going on? If you are having severe allergic reaction (food, bees, medication), call 911 now. Take your epinephrine as prescribed for allergic shock (anaphylaxis). For non-urgent matters, diphenhydramine is plenty strong for most mild allergies (and can cause drowsiness - don't drive). Many less strong antihistamines are over the counter. If not work - time to make an appointment with the provider.